All narcissists share certain traits. They are defined as people who have a grandiose idea of themselves, which simultaneously masks their low self-esteem. They present an inflated version of themselves outwards, which they believe is better than anyone around them, so they tend to treat others with contempt.

They are completely self-interested, and will only do something if they can see how it will benefit them.

However, what narcissitic people want to get from others differs between men and women, according to marriage and family therapist Margalis Fjelstad. She told Business Insider that typically, female narcissists are narcissistic about their looks, whereas for men, it's all about power and control.

"If it's a male narcissist, he is typically putting down his female partner and making her less powerful in order to make sure she stays with him," Fjelstad said. "Whereas female narcissists, if they're not happy with their partner, if they want more, they just go have an affair with somebody and find a more powerful partner."

This helps explain why there are more male narcissists.

Fjelstad thinks this is partly because we "still have a belief that men are superior."

"Men should make all the main choices in the family," she said, explaining how narcissists think, and the mistaken impression still around today that men should make all the decisions. "They should be the head of the house. We idealise and make men superior."

"The Narcissist Next Door" by Jeffrey Kluger also explores this idea. Kluger writes that as society is still predominantly patriarchal, we are more likely to tolerate narcissism and aggressiveness from men than women.

Narcissists are not usually violent — they're very good at controlling their emotions, and manipulating others into looking like they are hysterical. They're much more likely to use their brains to get their way, rather than physical force.

Male narcissists can dominate others via manipulation or games, whereas female narcissists use their sexual charm to get what they want, Fjelstad said.

Narcissists are fairly money-focused, because they believe it gives them status and dominance over others. However, men will be preoccupied with obtaining money via any route, including theft from their own family, whereas women are more interested in excessively spending money — not necessarily their own.

However, for all their differences, narcissistic men and women have a lot in common, too. A large study from the University of Buffalo in 2015 analysed 31 years of research on narcissism. While there were differences, such as men scoring higher in leadership and authority traits, there was little difference in vanity, self-absorption, and attention-seeking.